The need for communication is an essential factor shaping the physical nature of a computing system. A computing system functions by bringing a large number of separate elements to bear on a common problem. Coordinated operation of the elements requires a large amount of communication among them through many long wires. Some implications of communication for the physical characteristics of electrical computers are as follows. Variability in manufacturing and of the environment within a system causes the elements of a system to differ from one another in their responses to electrical signals. Signals must be large enough to be interpretable by any element of the system. Therefore, the need for rapid reliable communication implies that signals that are large in some sense are required. The combination of large signals and many wires implies high-power dissipation. Fitting the pattern of interconnection into minimum space is a very complex problem which is one of the most severe limitations on the utilization of integrated electronics in computation. Experience has led to the establishment of certain quantitative generalizations concerning the communication requirements in large systems. Similarity between these and neuronal communication is noted. © 1982 Plenum Publishing Corporation.